Vacuum carbon impregnation equipment

Abstract

To provide a vacuum carburization apparatus which reduces variation of carburization in upstream and downstream sides without excessively supplying carburization gas.SOLUTION: A vacuum carburization apparatus includes a furnace body 2 accommodating a work-piece 8, a plurality of supply ports 41, 42, 43 which supply gas into the furnace body 2, a carburization gas flow rate controller 13 which controls a supply flow rate of carburization gas G1, a plurality of open-close valves 31, 32, 33 which are disposed between the carburization gas flow rate controller 13 and the supply ports, respectively, and open and close a flow passage of the gas, an exhaust port 51 which discharges the gas within the furnace body 2, and a purge gas flow rate controller 23 which controls a supply flow rate of purge gas G2 for carrying out a purge process for purging the carburization gas G1 used in a vacuum carburization treatment. The purge process has a low flow rate purge period in which the supply flow rate of the purge gas G2 is lowered.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a vacuum carburizing apparatus. [Background technology]

[0002] As prior art for vacuum carburizing equipment, for example, Patent Documents 1 and 2 disclose spraying carburizing gas in one direction from multiple supply ports. Patent Document 3 discloses switching the supply of carburizing gas through multiple supply ports at different times. Patent Document 4 discloses providing supply ports for areas that are difficult for the carburizing gas to reach.

[0003] In vacuum carburizing equipment, the carburizing gas flows from the upstream side (supply port side) to the downstream side (exhaust port side), and the carburizing gas is consumed first by the upstream workpiece, so the carburizing gas concentration downstream is lower than the carburizing gas concentration upstream. Therefore, in order to obtain an appropriate carburizing gas concentration downstream as well, the carburizing gas is often supplied in excess of the appropriate amount calculated from the total surface area of ​​the workpiece. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-268365 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-206895 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-336469 [Patent Document 4] Japanese Patent Application Publication No. 2019-85623 Summary of the Invention [Problem to be solved by the invention]

[0005] Supplying more than the appropriate amount of carburizing gas increases running costs and increases the frequency of equipment maintenance due to the increased amount of carbonaceous components adhering to the furnace and exhaust system. On the other hand, if the amount of carburizing gas supplied is insufficient, workpieces are more likely to be poorly carburized downstream where the carburizing gas cannot reach.

[0006] There is a need for a vacuum carburizing apparatus that reduces the carburizing variation on the upstream and downstream sides without supplying an excessive amount of carburizing gas.

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a vacuum carburizing apparatus that reduces the carburizing variations on the upstream and downstream sides without supplying an excessive amount of carburizing gas. [Means for solving the problem]

[0008] In order to solve the above problems, a vacuum carburizing apparatus according to one aspect of the present invention comprises: a furnace body for storing the workpiece; a plurality of supply ports for supplying gas into the furnace body; a carburizing gas flow rate controller for controlling the supply flow rate of the carburizing gas; a plurality of on-off valves disposed between the carburizing gas flow rate controller and the supply port, for opening and closing gas flow paths; an exhaust port for exhausting gas from inside the furnace body; a purge gas flow rate controller for controlling the supply flow rate of a purge gas for performing a purge process to expel the carburizing gas used in the vacuum carburizing process, The purge process is characterized by having a low flow rate purge period in which the supply flow rate of the purge gas is reduced. [Effects of the Invention]

[0009] According to this invention, a high concentration of carburizing gas that enables appropriate vacuum carburizing processing is delivered to the downstream side without supplying an excessive amount of carburizing gas, thereby reducing carburizing variations between the upstream and downstream sides. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram for explaining a vacuum carburization apparatus and a vacuum carburization process according to a first embodiment. [Figure 2] 1. FIG. 4 is a diagram illustrating another vacuum carburization process using the vacuum carburization apparatus shown in FIG. [Figure 3] FIG. 10 is a diagram illustrating a purging process performed after a vacuum carburizing process. [Figure 4] FIG. 10 is a diagram for explaining a schematic diagram of a vacuum carburizing apparatus according to a second embodiment. [Figure 5] FIG. 5 is a diagram illustrating a purging process using the vacuum carburizing apparatus shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of a vacuum carburizing apparatus 1 according to the present invention will be described below with reference to the drawings. In the following description, terms indicating specific directions or positions (e.g., terms including "upper," "lower," "right," "left," "front," and "rear") will be used as necessary. However, these terms are used solely to facilitate understanding of the present disclosure with reference to the drawings and are not intended to limit the technical scope of the present disclosure. The terms "upstream" and "downstream" are used, and the "upstream" refers to the side of the gas supply port, and the "downstream" refers to the side of the gas discharge port, based on the gas flow direction. The following description is essentially merely illustrative and is not intended to limit the present disclosure, its applications, or its uses. Furthermore, the drawings are schematic, and the dimensional ratios and other characteristics may not necessarily correspond to actual values. In the drawings, valves shaded in black indicate the closed state, while valves shaded in white indicate the open state. In the drawings, the flow of carburizing gas is indicated by dashed lines, and the flow of purge gas is indicated by solid lines.

[0012] First Embodiment A vacuum carburizing apparatus 1 according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram for schematically explaining the vacuum carburizing apparatus 1 according to the first embodiment and the vacuum carburizing process.

[0013] As shown in Figure 1, the vacuum carburizing apparatus 1 is an apparatus that stores a workpiece 8, which is the material to be treated, inside a furnace body 2, heats it to a predetermined temperature, and performs vacuum carburizing treatment using carburizing gas G1 that flows inside the furnace body 2 under reduced pressure.

[0014] The gases used in the present invention are carburizing gas G1 and purge gas G2. Carburizing gas G1 is a hydrocarbon gas, such as acetylene gas, that reacts with the surface of the workpiece 8 to produce carbon. Purge gas G2 is an inert gas, such as nitrogen, that is used to expel and replace low-concentration carburizing gas G1 from the furnace body 2 when carbon diffusion treatment is performed after vacuum carburizing treatment.

[0015] In the vacuum carburizing apparatus 1, during vacuum carburizing treatment, carburizing gas G1 is supplied into the furnace body 2 through a carburizing gas supply source 11, while being discharged to the outside of the furnace body 2 by a vacuum pump 4. During vacuum carburizing treatment, the interior of the furnace is maintained at a substantially constant reduced pressure of, for example, about 1 kPa.

[0016] The vacuum carburizing apparatus 1 includes at least a furnace body 2, a plurality of supply ports 41, 42, 43, a carburizing gas flow controller 13, a purge gas flow controller 23, a plurality of on-off valves 31, 32, 33, and an exhaust port 51.

[0017] The furnace body 2 accommodates the workpiece 8 and has, for example, a substantially rectangular parallelepiped shape. The furnace body 2 is provided with a plurality of supply ports 41, 42, 43, for example, a first supply port 41, a second supply port 42, and a third supply port 43. Gases such as carburizing gas G1 and purge gas G2 are supplied into the furnace body 2 through the first supply port 41, the second supply port 42, and the third supply port 43. The furnace body 2 is provided with an exhaust port 51, for example, a first exhaust port 51. Gas that has flowed inside the furnace body 2 is constantly exhausted through the first exhaust port 51.

[0018] The furnace body 2 is equipped with a heating unit such as a heater, a thermometer for measuring the temperature inside the furnace, a pressure gauge for measuring the pressure inside the furnace, and a jig for placing multiple workpieces 8, all of which are not shown. A gas supply unit 7 is provided upstream of the furnace body 2, and a gas exhaust unit 9 is provided downstream of the furnace body 2. The gas supply unit 7 has a carburizing gas supply unit 10 and a purge gas supply unit 20.

[0019] The carburizing gas supply unit 10 comprises, from upstream to downstream, a carburizing gas supply source 11, a carburizing gas on-off valve 12, and a carburizing gas flow controller 13. The carburizing gas supply source 11 is composed of a gas cylinder or the like containing carburizing gas G1, such as acetylene gas. The carburizing gas on-off valve 12 is a valve that opens and closes the carburizing gas flow path through which the carburizing gas G1 flows, and is, for example, a solenoid valve whose opening and closing is controlled by a control unit (not shown). The carburizing gas flow controller 13 is a flow regulation valve that controls the supply flow rate of the carburizing gas G1, and is, for example, a mass flow controller that measures the mass flow rate of the carburizing gas G1 and controls the supply flow rate. The carburizing gas flow path from the carburizing gas supply source 11 to the carburizing gas flow controller 13 is connected by piping.

[0020] The purge gas supply unit 20 has, from upstream to downstream, a purge gas supply source 21, a purge gas on-off valve 22, and a purge gas flow controller 23. The purge gas supply source 21 is composed of a gas cylinder or the like containing purge gas G2 such as nitrogen gas. The purge gas on-off valve 22 is a valve that opens and closes a purge gas flow path through which the purge gas G2 flows, and is, for example, an electromagnetic valve whose opening and closing is controlled by a control unit (not shown). The purge gas flow controller 23 is a flow control valve that adjusts the flow rate of the purge gas G2, and is, for example, a mass flow controller that measures the mass flow rate of the purge gas G2 and controls the flow rate. The purge gas flow path from the purge gas supply source 21 to the purge gas flow controller 23 is connected by piping.

[0021] A confluent flow path 14 is formed by the carburizing gas flow path located downstream of the carburizing gas flow controller 13 and the purge gas flow path located downstream of the purge gas flow controller 23. The confluent flow path 14 is connected to a branch flow path 15 at a confluent point. The branch flow path 15 is formed by multiple flow paths leading from the confluent point to multiple supply ports 41, 42, and 43. The confluent flow path 14 and the branch flow paths 15 are configured by piping.

[0022] The multiple on-off valves 31, 32, and 33 provided include, for example, a first on-off valve 31, a second on-off valve 32, and a third on-off valve 33. Each on-off valve 31, 32, and 33 opens and closes a gas flow path, and is, for example, a solenoid valve whose opening and closing is controlled by a control unit (not shown). The first on-off valve 31 is provided in a branch flow path extending from the carburizing gas flow controller 13 to a first supply port 41, the second on-off valve 32 is provided in a branch flow path extending from the carburizing gas flow controller 13 to a second supply port 42, and the third on-off valve 33 is provided in a branch flow path extending from the carburizing gas flow controller 13 to a third supply port 43.

[0023] A plurality of supply ports 41, 42, 43 are arranged on the wall surface on the upstream side of the furnace body 2 (the wall surface on the left side in FIG. 1). The plurality of supply ports 41, 42, 43 include, for example, a first supply port 41, a second supply port 42, and a third supply port 43. Each of the supply ports 41, 42, 43 is formed by a nozzle attached to a through-hole formed in the wall surface, and gas is supplied into the furnace body 2 through each of the supply ports 41, 42, 43. The supply ports 41, 42, 43 are arranged spaced apart in an intersecting direction (the vertical direction in FIG. 1) that intersects with the gas flow direction (the direction from left to right in FIG. 1).

[0024] A first exhaust port 51 serving as an exhaust port is disposed on the downstream wall surface of the furnace body 2 (the wall surface on the right side in FIG. 1). The first exhaust port 51 is configured by a nozzle attached to a through-hole formed in the wall surface, and gas inside the furnace body 2 is exhausted through the first exhaust port 51. The first exhaust port 51 is disposed in approximately the center of the cross direction (the vertical direction in FIG. 1) that intersects with the gas flow direction.

[0025] In the exhaust flow path located downstream of the first exhaust port 51, an exhaust on-off valve 6 and a vacuum pump 4 are arranged from upstream to downstream as a gas exhaust unit 9. The exhaust on-off valve 6 is a valve that opens and closes the exhaust flow path, and is, for example, a solenoid valve that opens and closes under the control of a control unit (not shown). The vacuum pump 4 evacuates the inside of the furnace body 2. Pipes are connected between the exhaust port 51 and the exhaust on-off valve 6, and between the exhaust on-off valve 6 and the vacuum pump 4, respectively. When performing vacuum carburizing treatment and purging treatment, these pipes maintain the inside of the furnace at a reduced pressure. To maintain a substantially constant reduced pressure inside the furnace, for example, the exhaust on-off valve 6 is opened, and its opening degree is controlled by a control unit (not shown).

[0026] In the above-described vacuum carburizing apparatus 1, if all of the multiple on-off valves 31, 32, and 33 are opened and carburizing gas G1 is supplied in a dispersed manner from all of the supply ports 41, 42, and 43, the flow rate of the carburizing gas G1 slows down, making it difficult for the carburizing gas G1 to reach the downstream workpiece 8. As a result, the contact time of the downstream workpiece 8 with the carburizing gas G1 is shortened, and the carburizing gas G1 is consumed by the upstream workpiece 8, reducing the concentration of the carburizing gas G1 on the downstream side, making it more likely that unevenness will occur between the carburizing on the upstream side and the carburizing on the downstream side.

[0027] Therefore, as a first embodiment that solves this problem, a vacuum carburization process using the above-mentioned vacuum carburization apparatus 1 will be described with reference to FIGS.

[0028] 1 shows that, with the supply flow rate of carburizing gas G1 by the carburizing gas flow rate controller 13 kept constant, the carburizing gas on-off valve 12 in the gas supply unit 7 is open, the purge gas on-off valve 22 is closed, and one of the multiple on-off valves 31, 32, and 33 is open while the remaining on-off valves are closed. For example, the first on-off valve 31 is open, while the second on-off valve 32 and the third on-off valve 33 are closed. The carburizing gas flow rate controller 13 supplies an appropriate amount of carburizing gas G1 as the supply flow rate calculated from the total surface area of ​​the workpieces 8 placed inside the furnace body 2.

[0029] The carburizing gas flow rate controller 13 keeps the supply flow rate of the carburizing gas G1 constant, and the second on-off valve 32 and the third on-off valve 33 are closed. All of the on-off valves 31, 32, and 33 are connected to the three branched flow paths 15, respectively. Therefore, the carburizing gas G1 is ejected through the first supply port 41 connected to the open first on-off valve 31, and the carburizing gas G1 is ejected more forcefully than when all of the on-off valves 31, 32, and 33 are open and the gas is ejected in a dispersed manner. Because the flow rate of the carburizing gas G1 ejected from the first supply port 41 is increased, a high-concentration carburizing gas G1 reaches the workpiece 8 located downstream, away from the first supply port 41 (in other words, located on the side of the first discharge port). At this time, even if the flow rate of the carburizing gas G1 increases, the supply of the appropriate amount of carburizing gas G1 calculated from the total surface area of ​​the workpiece 8 is maintained, and the carburizing gas G1 forcefully ejected from the first supply port 41 diffuses inside the furnace, supplying the appropriate amount of carburizing gas G1 to the workpiece 8 located far from the first supply port 41. This state is continued for a predetermined time, and vacuum carburizing treatment is performed through the first supply port 41. As a result, a high concentration of carburizing gas G1 that enables appropriate vacuum carburizing treatment is delivered to the downstream side without supplying an excessive amount of carburizing gas G1, reducing carburizing variation between the upstream and downstream sides.

[0030] Although the carburizing gas G1 forcefully ejected from the first supply port 41 diffuses within the furnace, ejection from only one location results in a biased concentration distribution of the carburizing gas G1 in a direction intersecting the flow direction of the carburizing gas G1. Therefore, for example, the second on-off valve 32 is opened and the first on-off valve 31 and the third on-off valve 33 are closed at predetermined valve switching intervals. The carburizing gas G1 is forcefully ejected through the second supply port 42 connected to the open second on-off valve 32. Because the flow velocity of the carburizing gas G1 ejected from the second supply port 42 increases, the high-concentration carburizing gas G1 reaches the workpiece 8 located downstream, away from the second supply port 42. This state is maintained for a predetermined time, and vacuum carburizing is performed through the second supply port 42.

[0031] Then, at predetermined valve switching intervals, for example, the third on-off valve 33 is opened and the first on-off valve 31 and the second on-off valve 32 are closed. Carburizing gas G1 is forcefully ejected through the third supply port 43 connected to the open third on-off valve 33. As the flow rate of the carburizing gas G1 ejected from the third supply port 43 increases, the highly concentrated carburizing gas G1 reaches the workpiece 8 located downstream and away from the third supply port 43. This state is continued for a predetermined time, and vacuum carburizing treatment is carried out through the third supply port 43.

[0032] Then, at a predetermined valve switching interval, for example, the first on-off valve 31 is opened again, and the second on-off valve 32 and the third on-off valve 33 are closed. The carburizing gas G1 is forcefully ejected through the first supply port 41 connected to the open first on-off valve 31. The flow rate of the carburizing gas G1 ejected from the first supply port 41 increases, so that the highly concentrated carburizing gas G1 reaches the workpiece 8 located downstream and away from the first supply port 41. This state is continued for a predetermined time, and vacuum carburizing treatment is carried out through the first supply port 41.

[0033] In this manner, the closed state of any two of the multiple on-off valves 31, 32, and 33 is sequentially switched. In other words, the open state of any one of the multiple on-off valves 31, 32, and 33 is sequentially switched. As a result, vacuum carburizing treatment through the first supply port 41, vacuum carburizing treatment through the second supply port 42, and vacuum carburizing treatment through the third supply port 43 is sequentially switched at a predetermined valve switching interval. This switching operation is repeated multiple times. The predetermined valve switching interval is determined based on the furnace pressure and the supply flow rate of the carburizing gas G1. However, if the valve switching interval is too long, uneven carburizing is likely to occur due to the bias in the concentration distribution of the carburizing gas G1, as described above. On the other hand, if the valve switching interval is too short, uneven carburizing is likely to occur due to the high-concentration carburizing gas G1 not reaching the workpiece 8 located downstream. Therefore, a suitable valve switching interval is, for example, 1 to 15 seconds. This makes it possible to suppress unevenness in the concentration distribution of the carburizing gas G1 inside the furnace body 2, and to suppress uneven carburizing.

[0034] Figure 2 is a diagram illustrating another vacuum carburizing process using the vacuum carburizing apparatus 1 shown in Figure 1. Figure 2 shows that, with the carburizing gas flow rate controller 13 supplying a constant flow rate of carburizing gas G1, the carburizing gas on-off valve 12 in the gas supply unit 7 is open, the purge gas on-off valve 22 is closed, and two of the multiple on-off valves 31, 32, and 33 are open while the remaining on-off valves are closed. For example, the second on-off valve 32 and the third on-off valve 33 are open, and the first on-off valve 31 is closed. The carburizing gas flow rate controller 13 supplies an appropriate amount of carburizing gas G1 as the supply flow rate calculated from the total surface area of ​​the workpieces 8 placed inside the furnace body 2.

[0035] The supply flow rate of carburizing gas G1 by the carburizing gas flow rate controller 13 is kept constant, and the first on-off valve 31 is closed. Therefore, carburizing gas G1 is ejected through the second supply port 42 and the third supply port 43 connected to the open second on-off valve 32 and the third on-off valve 33, respectively. However, the carburizing gas G1 is ejected more forcefully than when all of the on-off valves 31, 32, and 33 are open. Because the flow rate of the carburizing gas G1 ejected from the second supply port 42 and the third supply port 43 is increased, high-concentration carburizing gas G1 reaches the workpiece 8 located downstream and away from the second supply port 42 and the third supply port 43. This state is continued for a predetermined time, and vacuum carburizing processing is performed through the second supply port 42 and the third supply port 43. This allows a high concentration of carburizing gas G1 to be delivered downstream, enabling appropriate vacuum carburizing processing without supplying an excessive amount of carburizing gas G1, thereby reducing carburizing variations between the upstream and downstream sides.

[0036] Although the carburizing gas G1 forcefully ejected from the first supply port 41 diffuses within the furnace, ejection from only one location results in a biased concentration distribution of the carburizing gas G1 in a direction intersecting the flow direction of the carburizing gas G1. Therefore, for example, the first and third on-off valves 31 and 33 are opened and the second on-off valve 32 is closed at predetermined valve switching intervals. The carburizing gas G1 is forcefully ejected through the first and third supply ports 41 and 43, which are connected to the open first and third on-off valves 31 and 33, respectively. Because the flow velocity of the carburizing gas G1 ejected from the first and third supply ports 41 and 43 increases, the high-concentration carburizing gas G1 reaches the workpiece 8 located downstream from the first and third supply ports 41 and 43. This state is maintained for a predetermined time, and vacuum carburizing is performed through the first and third supply ports 41 and 43.

[0037] Then, at predetermined valve switching intervals, for example, the first on-off valve 31 and the second on-off valve 32 are opened, and the third on-off valve 33 is closed. Carburizing gas G1 is forcefully ejected through the first supply port 41 and the second supply port 42 connected to the open first on-off valve 31 and the second on-off valve 32, respectively. Because the flow rate of the carburizing gas G1 ejected from the first supply port 41 and the second supply port 42 increases, high-concentration carburizing gas G1 reaches the workpiece 8 located downstream and away from the first supply port 41 and the second supply port 42. This state continues for a predetermined time, and vacuum carburizing treatment is performed through the first supply port 41 and the second supply port 42.

[0038] Then, at a predetermined valve switching interval, for example, the second on-off valve 32 and the third on-off valve 33 are opened again, and the first on-off valve 31 is closed. The carburizing gas G1 is forcefully ejected through the second supply port 42 and the third supply port 43 connected to the open second on-off valve 32 and the third on-off valve 33, respectively. Because the flow rate of the carburizing gas G1 ejected from the second supply port 42 and the third supply port 43 increases, the high-concentration carburizing gas G1 reaches the workpiece 8 located downstream and away from the second supply port 42 and the third supply port 43. This state is continued for a predetermined time, and vacuum carburizing treatment is performed through the second supply port 42 and the third supply port 43.

[0039] As described above, the closed state of any one of the multiple on-off valves 31, 32, and 33 is sequentially switched. In other words, the open state of any two of the multiple on-off valves 31, 32, and 33 is sequentially switched. As a result, vacuum carburizing treatment through the first supply port 41 and the second supply port 42, vacuum carburizing treatment through the second supply port 42 and the third supply port 43, and vacuum carburizing treatment through the first supply port 41 and the third supply port 43 are sequentially switched at a predetermined valve switching interval. This switching operation is repeated multiple times. As in the embodiment described with reference to FIG. 1, the predetermined valve switching interval is determined based on the furnace pressure and the supply flow rate of the carburizing gas G1. A suitable valve switching interval is, for example, 1 to 15 seconds. Note that, compared to the embodiment described with reference to FIG. 1, the flow rate of the carburizing gas G1 is slower, but is faster than when all of the on-off valves 31, 32, and 33 are open.

[0040] Next, the purging process performed after the vacuum carburizing process described above with reference to Figures 1 and 2 will be described with reference to Figure 3. Figure 3 is a diagram for explaining the purging process performed after the vacuum carburizing process.

[0041] 3 shows that purging is performed by closing the carburizing gas on-off valve 12 and opening the purge gas on-off valve 22 in the gas supply section 7, and by opening all on-off valves 31, 32, and 33, under a substantially constant reduced pressure inside the furnace. That is, FIG. 3 shows how, during the purging process, the carburizing gas G1 that had been present in the furnace until then is gradually pushed out toward the exhaust port 51 by the purge gas G2 flowing from upstream to downstream inside the furnace.

[0042] The above-described vacuum carburizing apparatus 1 performs a vacuum carburizing process under reduced pressure to penetrate carbon into the surface layer of the workpiece 8, followed by a diffusion process to thermally diffuse the carbon from the surface layer into the interior of the workpiece 8, repeating the vacuum carburizing and diffusion processes until a predetermined carburized depth and surface carbon concentration are achieved. In the diffusion process, the workpiece is heated to a predetermined temperature under reduced pressure, and the flow of carburizing gas G1 is interrupted and replaced with the flow of inert purge gas G2, for example, to thermally diffuse the carbon. In other words, the diffusion process includes a purge process to expel the carburizing gas G1 used during the vacuum carburizing process.

[0043] When replacing the carburizing gas G1 with the purge gas G2, in other words, when switching from vacuum carburizing to diffusion, if the supply flow rate of the purge gas G2 is approximately the same as that of the carburizing gas G1, the purge gas G2 will quickly reach the first exhaust port 51, shortening the time that the carburizing gas G1 remains on the side of the first exhaust port 51 (downstream side) and promoting dilution of the carburizing gas G1 downstream. Therefore, even when replacing the carburizing gas G1 with the purge gas G2, poor carburizing is likely to occur in the downstream workpiece 8.

[0044] Therefore, when replacing the carburizing gas G1 with the purge gas G2, the purge gas flow rate controller 23 is controlled so that the supply flow rate of the purge gas G2 is less than the supply flow rate of the carburizing gas G1. That is, the purge process performed after the vacuum carburizing process has a low-flow purge period in which the supply flow rate of the purge gas G2 is reduced. Because the purge gas G2 reaches the first exhaust port 51 slowly, the carburizing gas G1 is retained on the side of the first exhaust port 51 (downstream) for a longer period, and the dilution of the carburizing gas G1 downstream can be delayed. This increases the contact time between the workpiece 8 and the carburizing gas G1 downstream, suppressing a decrease in the concentration of the carburizing gas G1 downstream and suppressing poor carburizing of the workpiece 8 downstream.

[0045] The low-flow purge period, during which the supply flow rate of purge gas G2 is reduced, is defined as the time required, for example, from the start of supply of purge gas G2 until the concentration of carburizing gas G1 inside the furnace body 2 falls to 5% or less. This is because, when the concentration of carburizing gas G1 falls to 5% or less, the effectiveness of the carbon surface reaction is significantly reduced. In this way, the definition of the low-flow purge period allows quantitative management of the purge process.

[0046] Second Embodiment The vacuum carburizing apparatus 1 according to the second embodiment will be described with reference to Fig. 4. Fig. 4 is a diagram for explaining the vacuum carburizing apparatus 1 according to the second embodiment.

[0047] The vacuum carburizing apparatus 1 according to the second embodiment is characterized in that a plurality of supply ports 41, 42, 44, 45 are provided on one side and the other side of the furnace body 2, and discharge ports 51, 52 are provided on one side and the other side of the intersection of the one side and the other side of the furnace body 2. The following mainly explains the differences from the vacuum carburizing apparatus 1 according to the first embodiment described above.

[0048] A first gas supply unit 7 is disposed upstream on one side (left side in FIG. 4) of the furnace body 2, and the first gas supply unit 7 has a first carburizing gas supply unit 10 and a first purge gas supply unit 20. A second gas supply unit 7 is disposed upstream on the other side (right side in FIG. 4) of the furnace body 2, and the second gas supply unit 7 has a second carburizing gas supply unit 10 and a second purge gas supply unit 20.

[0049] 4, when the furnace body 2 has a substantially rectangular parallelepiped shape, a first supply port 41 and a second supply port 42 connected to a gas supply unit 7 on one side are disposed on a wall surface on one side of the furnace body 2, and a fourth supply port 44 and a fifth supply port 45 connected to a gas supply unit 7 on the other side are disposed on a wall surface on the other side of the furnace body 2. For example, the first supply port 41 and the fourth supply port 44 face each other, and the second supply port 42 and the fifth supply port 45 face each other.

[0050] The first exhaust port 51 is disposed on one side of the intersection of the furnace body 2 (upper side in FIG. 4), and the second exhaust port 52 is disposed on the other side of the intersection of the furnace body 2 (lower side in FIG. 4). For example, the first exhaust port 51 and the second exhaust port 52 face each other. A first exhaust flow path located downstream of the first exhaust port 51 and a second exhaust flow path located downstream of the second exhaust port 52 are connected to the exhaust flow path at an exhaust junction point. In the exhaust flow path, an exhaust on-off valve 6 and a vacuum pump 4 are disposed from upstream to downstream as a gas exhaust unit 9.

[0051] In the above-described vacuum carburizing apparatus 1, the carburizing gas G1 reaches workpieces 8 located in the intermediate region of the furnace body 2 less easily than workpieces 8 located near the first and second supply ports 41 and 42 and the fourth and fifth supply ports 44 and 45. As a result, the contact time of workpieces 8 located in the intermediate region of the furnace body 2 with the carburizing gas G1 is shorter, and the carburizing gas G1 is consumed by workpieces 8 located near the first and second supply ports 41 and 42 and the fourth and fifth supply ports 44 and 45, reducing the concentration of carburizing gas G1 in the intermediate region of the furnace body 2. This makes it more likely that non-uniformity will occur between the carburizing in the regions near the supply ports 41, 42, 44, and 45 and the carburizing in the intermediate region of the furnace body 2.

[0052] Therefore, as a second embodiment that solves this problem, a vacuum carburizing process using the above-mentioned vacuum carburizing apparatus 1 will be described with reference to FIG.

[0053] 4 shows that, while the supply flow rate of carburizing gas G1 by the carburizing gas flow controllers 13 on one side and the other side is kept substantially constant, the carburizing gas on-off valves 12 on one side and the other side of the gas supply units 7 on the other side are opened, and the purge gas on-off valves 22 on one side and the other side are closed. Also, one of the opposing on-off valves 31, 34; 32, 35 on one side and the other side is opened, while the other is closed. For example, the first on-off valve 31 on one side and the fourth on-off valve 34 on the other side are opened, and the second on-off valve 32 on one side and the fifth on-off valve 35 on the other side are closed. The carburizing gas flow controllers 13 on one side and the other side supply an appropriate amount of carburizing gas G1 as the supply flow rate calculated from the total surface area of ​​the workpieces 8 placed in the furnace chamber 2.

[0054] The supply flow rate of the carburizing gas G1 by the carburizing gas flow rate controllers 13, 13 on one side and the other side is kept substantially constant, and the second on-off valve 32 on one side and the fifth on-off valve 35 on the other side are closed. Therefore, the carburizing gas G1 is forcefully ejected through the first supply port 41 on one side connected to the open first on-off valve 31, and through the fourth supply port 44 on the other side connected to the open fourth on-off valve 34.

[0055] The carburizing gas G1 on one side ejected from the first supply port 41 and the carburizing gas G1 on the other side ejected from the fourth supply port 44 collide in an intermediate region located approximately halfway between the one and other sides of the furnace body 2. This allows a high concentration of carburizing gas G1 to reach the workpiece 8 on one side located near the first supply port 41, the workpiece 8 on the other side located near the fourth supply port 44, and the workpiece 8 located in the intermediate region of the furnace body 2. This state is continued for a predetermined time, and vacuum carburizing treatment is performed through the first supply port 41 and the fourth supply port 44. As a result, high concentration carburizing gas G1 that enables appropriate vacuum carburizing treatment is delivered to the intermediate region of the furnace body 2 without supplying an excessive amount of carburizing gas G1, reducing carburizing variation regardless of the position inside the furnace body 2.

[0056] Then, at a predetermined valve switching interval, for example, the second on-off valve 32 on one side and the fifth on-off valve 35 on the other side are opened, while the first on-off valve 31 on one side and the fourth on-off valve 34 on the other side are closed. Carburizing gas G1 is forcefully ejected through the second supply port 42 on one side, which is connected to the open second on-off valve 32, and through the fifth supply port 45 on the other side, which is connected to the open fifth on-off valve 35. The carburizing gas G1 ejected from the second supply port 42 on one side and the carburizing gas G1 ejected from the fifth supply port 45 on the other side collide in the middle region of the furnace body 2. This allows high-concentration carburizing gas G1 to reach the workpiece 8 located in the middle region of the furnace body 2. This state is continued for a predetermined time, and vacuum carburizing processing is performed through the second supply port 42 and the fifth supply port 45.

[0057] Then, at a predetermined valve switching interval, for example, the first on-off valve 31 and the fourth on-off valve 34 are opened again, and the second on-off valve 32 and the fifth on-off valve 35 are closed. As above, the carburizing gas G1 ejected on one side from the first supply port 41 and the carburizing gas G1 ejected on the other side from the fourth supply port 44 collide in the intermediate region of the furnace body 2, and high-concentration carburizing gas G1 reaches each workpiece 8 located in the intermediate region of the furnace body 2. This state is continued for a predetermined time, and vacuum carburizing treatment is performed through the first supply port 41 and the fourth supply port 44.

[0058] As described above, one of the opposing on-off valves on one side and the other side is sequentially opened and the other is closed. Therefore, vacuum carburizing treatment through the first supply port 41 and the fourth supply port 44 and vacuum carburizing treatment through the second supply port 42 and the fifth supply port 45 are sequentially switched at a predetermined valve switching interval, for example, at intervals of 1 to 15 seconds. This switching operation is repeated multiple times.

[0059] Next, the purging process carried out after the above-mentioned vacuum carburizing process using the vacuum carburizing apparatus 1 shown in Fig. 4 will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining the purging process using the vacuum carburizing apparatus 1 shown in Fig. 4.

[0060] FIG. 5 shows that the purging process is performed by closing the carburizing gas valve 12 in the gas supply section 7, opening the purge gas valve 22, and opening all the valves 31, 32, 34, and 35, under a substantially constant reduced pressure inside the furnace.

[0061] As in the purging process described in the first embodiment, when replacing carburizing gas G1 with purge gas G2, the one-side and other purge gas flow rate controllers 23, 23 are controlled so that the supply flow rate of purge gas G2 is less than the supply flow rate of carburizing gas G1. Because the one-side and other purge gases G2, G2 reach the intermediate region slowly, the highly concentrated carburizing gas G1 is retained for a longer period in the intermediate region of the furnace body 2, and the dilution of carburizing gas G1 in the intermediate region of the furnace body 2 is delayed. This lengthens the contact time between the workpieces 8 and the carburizing gas G1 in the intermediate region of the furnace body 2, suppressing the decrease in the concentration of carburizing gas G1 and thereby suppressing the occurrence of poor carburization of the workpieces 8 located in the intermediate region of the furnace body 2. The low-flow purge period during which the supply flow rate of purge gas G2 is reduced is defined, for example, as the time required for the concentration of carburizing gas G1 inside the furnace body 2 to fall to 5% or less, starting from the start of supply of purge gas G2. This is because the effect of the surface reaction of carbon is significantly reduced when the concentration of carburizing gas G1 is reduced to 5% or less by purge gas G2. In this way, the purging process can be quantitatively controlled by specifying the low-flow purge period.

[0062] Although specific embodiments of the present invention have been described, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0063] In the vacuum carburizing apparatus 1 of the above embodiment, multiple on-off valves 31, 32, 33 are provided near the multiple supply ports 41, 42, 43, and at least one of these on-off valves is closed to increase the flow rate of the carburizing gas G1 sprayed from the open supply ports. Alternatively, multiple exhaust ports may be provided for one supply port, and multiple on-off valves corresponding to the multiple exhaust ports may be provided, and at least one of these on-off valves may be closed to increase the flow rate of the carburizing gas G1 discharged from the open exhaust port (in other words, sucked in by the vacuum pump 4), thereby ultimately increasing the flow rate of the carburizing gas G1 sprayed from the supply port.

[0064] In the above embodiment, the furnace body 2 is exemplified as having an approximately rectangular parallelepiped shape, but for example, the furnace body 2 can also have an approximately cylindrical shape, with multiple supply ports 41, 42, 43 arranged on one side of the cylindrical shape and a discharge port 51 arranged on the other side.

[0065] In the above embodiment, the valve switching intervals of the on-off valves may be the same predetermined time, or may be different times depending on the ease of flow of the carburizing gas G1 inside the furnace body 2.

[0066] In the above embodiment, the carburizing gas flow rate controller 13 and the purge gas flow rate controller 23 may be combined into one controller.

[0067] In the above embodiment, the first discharge ports 51 may be provided at a plurality of locations in the furnace body 2.

[0068] In the above embodiment, pressure control using the exhaust on-off valve 6 is performed when the inside of the furnace is maintained at a substantially constant reduced pressure, but pressure control may be performed by providing a separate pressure control valve or by controlling the exhaust capacity of the vacuum pump 4. Also, if the inside of the furnace is in a reduced pressure state, it is not necessary to control the pressure to a substantially constant value.

[0069] The first discharge port 51 and the second discharge port 52 may be disposed on either side of the furnace body 2, that is, on one crossing side (upper side in FIG. 4) or the other crossing side (lower side in FIG. 4).

[0070] The supply flow rate of the carburizing gas G1 is an appropriate amount calculated from the total surface area of ​​the workpieces 8 placed inside the furnace body 2. This appropriate amount is intended to be a supply amount that allows for uniform carburizing of the workpieces 8, and in reality, it is an amount that is a constant multiplied by the amount calculated from the total surface area of ​​the workpieces 8.

[0071] The present invention and its embodiments can be summarized as follows.

[0072] The vacuum carburizing apparatus 1 according to the first aspect of the present invention comprises: a furnace body 2 for storing the workpiece 8; A plurality of supply ports 41, 42, 43: 41, 42, 44, 45 for supplying gas into the furnace body 2; a carburizing gas flow rate controller 13 for controlling the supply flow rate of the carburizing gas G1; a plurality of on-off valves 31, 32, 33; 31, 32, 34, 35, respectively disposed between the carburizing gas flow rate controller 13 and the supply port, for opening and closing the gas flow path; An exhaust port 51:51, 52 for discharging gas inside the furnace body 2; a purge gas flow rate controller 23 for controlling the supply flow rate of a purge gas G2 for performing a purge process to expel the carburizing gas G1 used in the vacuum carburizing process; The purge process is characterized by having a low flow rate purge period in which the supply flow rate of the purge gas G2 is reduced.

[0073] According to the above embodiment, the purge gas G2 slowly reaches the exhaust ports 51:51, 52, and the high-concentration carburizing gas G1 remains on the side of the exhaust ports 51:51, 52 for a long time, thereby preventing poor carburizing of the downstream workpiece 8. Therefore, without supplying an excess of carburizing gas G1, the high-concentration carburizing gas G1 that enables appropriate vacuum carburizing processing is also delivered to the downstream side, reducing carburizing variations between the upstream and downstream sides.

[0074] Further, the vacuum carburizing apparatus 1 according to the second aspect is the same as that according to the first aspect, The low flow rate purge period is defined as the time required from the start of supply of the purge gas G2 until the concentration of the carburizing gas G1 inside the furnace body 2 becomes 5% or less.

[0075] According to the above embodiment, when the concentration of the carburizing gas G1 is reduced to 5% or less by the purge gas G2, the effect of the surface reaction of carbon is significantly reduced, so the purge process can be quantitatively controlled by specifying the low flow rate purge period.

[0076] Further, the vacuum carburizing apparatus 1 according to the third aspect is the same as that according to the first or second aspect, At least one of the plurality of on-off valves 31, 32, 33; 31, 32, 34, 35 is closed to perform the vacuum carburization treatment.

[0077] According to the above embodiment, the carburizing gas G1 is supplied vigorously from any one of the multiple supply ports 41, 42, 43: 41, 42, 44, 45, so that the carburizing gas G1 is not supplied in excess and a high concentration of the carburizing gas G1 that enables appropriate vacuum carburizing processing is delivered to the downstream side as well, thereby reducing the variation in carburizing between the upstream and downstream sides.

[0078] Further, the vacuum carburizing apparatus 1 according to the fourth aspect is the same as that according to the first aspect, The vacuum carburizing treatment is carried out under the condition that the supply flow rate of the carburizing gas G1 by the carburizing gas flow rate controller 13 is constant.

[0079] According to the above aspect, it is possible to carry out a vacuum carburizing process with higher accuracy.

[0080] Further, the vacuum carburizing apparatus 1 according to the fifth aspect is the same as that according to the third aspect, The on-off valves 31, 32, 33: 31, 32, 34, 35 are sequentially switched to closed or not.

[0081] According to the above embodiment, the carburizing gas G1 is sequentially supplied from any one of the plurality of supply ports 41, 42, 43: 41, 42, 44, 45, so that the carburizing variation in the direction intersecting the flow direction of the carburizing gas G1 can be reduced.

[0082] Further, the vacuum carburizing apparatus 1 according to the sixth aspect is the same as that according to the fifth aspect, The valve switching interval for switching the on-off valves 31, 32, 33; 31, 32, 34, 35 between on and off is 1 second to 15 seconds.

[0083] According to the above embodiment, it is possible to suppress the unevenness of the concentration distribution of the carburizing gas G1 inside the furnace body 2, and it is possible to suppress uneven carburizing. [Explanation of symbols]

[0084] 1...Vacuum carburizing equipment 2…Furnace body 4...Vacuum pump 6...Exhaust valve 7...Gas supply section 8...Work 9...Gas exhaust section 10...Carburizing gas supply section 11...Carburizing gas supply source 12...Carburizing gas on-off valve 13...Carburizing gas flow controller 14...Confluence channel 15...Branch channel 20...Purge gas supply unit 21...Purge gas supply source 22...Purge gas on-off valve 23...Purge gas flow controller 31...First on-off valve (on-off valve) 32...Second on-off valve (on-off valve) 33...Third on-off valve (on-off valve) 34...Fourth on-off valve (on-off valve) 35...5th on-off valve (on-off valve) 41...First supply port (supply port) 42...Second supply port (supply port) 43...Third supply port (supply port) 44...Fourth supply port (supply port) 45...5th supply port (supply port) 51...1st discharge port (discharge port) 52…Second discharge port (discharge port) G1...Carburizing gas G2...Purge gas

Claims

1. a furnace body for storing the workpiece; a plurality of supply ports for supplying gas into the furnace body; a carburizing gas flow rate controller for controlling the supply flow rate of the carburizing gas; a plurality of on-off valves disposed between the carburizing gas flow rate controller and the supply port, for opening and closing gas flow paths; an exhaust port for exhausting gas from inside the furnace body; a purge gas flow rate controller for controlling the supply flow rate of a purge gas for performing a purge process to expel the carburizing gas used in the vacuum carburizing process, The supply port is provided only on one side wall surface of the furnace body, The outlet is provided on the other wall surface opposite to the one wall surface, The vacuum carburizing apparatus is characterized in that the purging process includes a low flow rate purging period in which the supply flow rate of the purge gas is made smaller than the supply flow rate of the carburizing gas.

2. 2. The vacuum carburizing apparatus according to claim 1, wherein the low flow rate purge period is defined as the time required for the concentration of the carburizing gas inside the furnace body to become 5% or less, starting from the start of supply of the purge gas.

3. 2. The vacuum carburizing apparatus according to claim 1, wherein the vacuum carburizing treatment is carried out under a condition where the flow rate of the carburizing gas supplied by the carburizing gas flow rate controller is constant.

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